Rotary impact wrench mechanism

ABSTRACT

A ROTARY IMPACR WRENCH CLUTCH MECHANISM INCLUDING A ROTARY ANVIL ADAPTED TO DELIVER A ROTARY BLOW TO A FASTENER, A ROTARY HAMMER CARRIED MOUNTED AROUND THE ANVIL AND CONNECTED TO A MOTOR, AND A PAIR OF DIAMETRICALLY OPPOSED HAMMER DOGS PICOTED ON THE CARRIER TO TILT INWARDLY TO STRIKE A BLOW TO THE ANVIL. THE CLUTCH MECHANISM INCLUDES A CAM OPERATIVE TO TILT THE HAMMER DOGS INWARDLY TO STRIKE A BLOW AND THEN TO ALLOW THE DOGS TO PASS THE ANVIL WITHOUT STRIKING A BLOW DURING THE FOLLOWING ROTATION OF THE CARRIER. THE HAMMER DOGS ARE PROPORTIONED AND PIVOTED SO THAT THEY AUTOMATICALLY REMAIN IN THE NON-IMPACT POSITION UNTIL THEY   ARE CAMMED INWARDLY AND THEY ARE RETURNED TO THE NONIMPACT POSITION DURING THEIR REBOUND BY INERTIAL FORCES FOLLOWING IMPACT WITH THE ANVIL. THE TOOL CLUTCH IS OPERATIVE IN EITHER DIRECTION OF ROTATION AND INCLUDES STOP MEANS FOR AUTOMATICALLY PREVENTING THE DOGS FROM TILTING IN THE WRONG DIRECTION IN EITHER DIRECTION OF ROTATION. DURING THE INSTANT OF IMPACT INERTIAL FORCES HOLD THE HAMMER DOGS AGAINST SLIDING OUT OF ENGAGEMENT WITH THE ANVIL.

Sept. 20, 1971 L. KRAMER ROTARY mmcr WRENCH MECHANISM 5 Sheets-Sheet 1Filed Aug. 23. 1968 INVENTOR L E 0 KRAMER ATTORNEY Sept. 20, 1'97! L.KRAMER noun-1 mmc'r wax-men uscnmsm 5 Sheets-Sheet 3 Filed Aug. 25, 1968FIG. 6

INVENTOR LEO mam-n BY M w .Tm

-FIG. 7

ATTORNEY Sept. 20, 1971 L. KRAMER noun! mnc'r vmmuca uncumsu 5Sheets-Sheet 5 Filed Aug. 23, 1968 m T N E V N LEO KRAMER J BY W wfrzumATTORNEY Sept. 20, 1911 L. mm 3.

ROTARY IMPACT 'WRENGH- IIEGHANISM Filed Aug. 23. 1968 5 Sheets-ShootINVENTOR LEO KRAMER ATTORNEY Sept. 20, 1971 I Kfi 3,605,914

7 ROTARY IMPACT WRENCH IECHANISM Filed 1mg. 2a, 1968 5 Sheets-Sheot-iINVENTOR LEO KRAMER ATTORNEY United States Patent O 3,605,914 ROTARYIMPACT WRENCH MECHANISM Leo Kramer, Skillman, N.J., assignor toIngersoll- Rand Company, New York, N.Y. Filed Aug. 23, 1968, Ser. No.754,824 Int. Cl. B25d /00 U.S. Cl. 173-93 31 Claims ABSTRACT OF THEDISCLOSURE A rotary impact wrench clutch mechanism including a rotaryanvil adapted to deliver a rotary blow to a fastener, a rotary hammercarrier mounted around the anvil and connected to a motor, and a pair ofdiametrically opposed hammer dogs pivoted on the carrier to tiltinwardly to strike a blow to the anvil. The clutch mechanism includes acam operative to tilt the hammer dogs inwardly to strike a blow and thento allow the dogs to pass the anvil without striking a blow during thefollowing rotation of the carrier. The hammer dogs are proportioned andpivoted so that they automatically remain in the non-impact positionuntil they are cammed inwardly and they are returned to the nonimpactposition during their rebound by inertial forces following impact withthe anvil. The tool clutch is operative in either direction of rotationand includes stop means for automatically preventing the dogs fromtilting in the wrong direction in either direction of rotation. Duringthe instant of impact inertial forces hold the hammer dogs againstsliding out of engagement with the anvil.

BACKGROUND OF INVENTION This invention relates to a power-operatedrotary impact wrench or impact tool for applying rotary or angularimpacts to fasteners such as threaded nuts, bolts, etc. In particular,this invention relates to a rotary impact tool mechanism for changingthe rotating torque of a rotary motor, such as an air-driven motor, to aseries of rapid rotary impacts which can be applied to a threaded nutfor either driving it tight or for removing it.

Most rotary impact mechanisms in use today contain an anvil adapted tobe connected to a wrench socket and a hammer rotated by a motor. Thehammer is alternately engaged and disengaged from the anvil, beingengaged to impact the anvil, thereafter being disengaged from the anvilto gather rotary speed again, prior to striking another impact to theanvil. Various means are used for accomplishing this alternateengagement and disengagement between the anvil and hammer.

One well known impact mechanism used today is known as the Pottmechanism, being named after the inventor who received US. Pat. Nos.2,012,916, 2,049,- 273 and 2,158,303. A modern version of the Pottmechanism is shown in the US. patent to Jimmerson No. 2,160,150. In theJimmerson patent, the hammer is mounted on a shaft driven by a motor andcam balls are mounted between the hammer and the shaft with the camballs resting in V-shaped grooves formed on the shaft with the cam ballsresting in V-shaped grooves formed on the shaft. Normally, a coil springbiases the hammer into engagement position with the anvil wherein thecam balls rest in the apexes of their grooves. After the hammer strikesthe anvil, the shaft continues to rotate and the relative rotationbetween the shaft and hammer causes the cam balls to ride up theirgroves and pull the hammer axially rearward to disengagement position,thus compressing and storing potential energy in the hammer biasingspring. When the hammer is disengaged from the anvil, the combinedenergy in the compressed spring and the rotating Patented Sept. 20, 1971"ice shaft turns the hammer forward to deliver another impact to theanvil.

The Pott mechanism has several disadvantages, one being that when a pairof diametrically opposed hammer dogs are used, the hammer strikes animpact each halfturn which prevents it from gaining sufiicient speedbetween impacts.

Another well known impact mechanism is disclosed in the US. patent toAmtsberg, No. 2,881,884. In this mechanism, the hammer is spring-biasedaxially away from the anvil to a disengaged position and cams operatedby the relative rotation between the anvil and hammer cause the hammerto be periodically thrown axially forward to strike a rotary impact withthe anvil. This mechanism is known as the ski-jump mechanism.

One disadvantage of the above Amtsberg ski-jump mechanism is that if thehammer is driven slower than its design speed, the hammer teeth will notbe thrown far enough anxially forward to engage the anvil teeth properlyupon impact. When the hammer teeth are not thrown far enough forward,they top, dub or barely strike the anvil jaws or teeth which causesrapid wear of such teeth. Another disadvantage of the above skipumpmechanism is that under certain conditions, it will rebound and strikethe anvil jaws several times after an initial impact before rotatingpast the anvil jaws and gaining speed for a following impact. Reboundingis wasteful of power and time and, thus, is undesirable.

A third mechanism is known as the swinging weight mechanism and isdisclosed in the US. Pat. No. 2,285,638 to Amtsberg. This mechanism usesa pair of diametrically opposed tilting hammer dogs which rotate arounda lobed anvil and are cammed into an impact position with the lobes orjaws on the anvil by engagement with the anvil. The hammer dogs arereleased by the cams on the anvil immediately before impact and means isprovided for applying a drive torque to the dogs to cause them to rotateto a disengaging position following an impact.

The swinging weight mechanism has the disadvantage of impacting eachhalf turn of the ham-mer, when two hammer dogs are used, thus preventingthe hammer from gaining sufficient speed between impacts. It isdesirable to provide a pair of hammer dogs so that the anvil willreceive a balanced blow, i.e., a pair of impacts delivered to theopposite sides of the anvil.

Another disadvantage of the swinging weight mechanism is that it oftenrebounds after impact and strikes a blow on its reverse stroke, which isvery undesirable, because not only is it inefiicient, but it is actingin the reverse rotary direction.

SUMMARY OF INVENTION The principal object of this invention is toprovide a rotary impact mechanism which overcomes the undesirablefeatures of the foregoing impact mechanisms and, in general,significantly advances the art of rotary impact wrenches.

Other important objects of this invention are: to provide a rotaryimpact tool which does not top or dub its dogs or teeth; to provide arotary impact tool which provides a balanced impact to the anvil whiledriving the hammer one full turn between impacts; to provide a rotaryimpact tool which does not strike any blows in either rotary directionduring rebound from an impact blow; to provida an impact mechanism usingradially tilting hammer dogs surrounding an anvil and having anon-impact position of the dogs wherein the hammer can rotate free ofthe anvil; to provide an impact mechanism having radially tilting hammerdogs and an automatic means for preventing the hammer dogs from tiltingin the wrong direction in either direction of operation; to

provide an impact mechanism having a radially tilting hammer dog whichautomatically tilts to its non-impact position following impact withoutthe application of torque to the pivot of the hammer dog; to provide animpact mechanism having a radially tilting hammer dog which is shaped,proportioned and has a mass which causes the creation of inertia forcesthat prevent the hammer dog from disengaging during the instant ofimpact; to provide an impact mechanism which can strike an initial blowwhich is stronger than the following normal blows; and to provide animpact mechanism having a hammer dog shaped and positioned to createinertial forces acting to move the hammer dog to its non-impactingposition relative to the anvil during rebound of the hammer dogfollowing impact with the anvil.

In general, the foregoing objects are attained in a rotary impactmechanism including an anvil carrying a pair of jaws, teeth or detents,a hammer carrier surrounding the anvil and carrying a pair ofdiametrically opposed tilting hammer dogs. Tht hammer dogs have a middleposition where they can rotate around the anvil without engaging it andcan be tilted to impact the anvil jaws in either direction of rotation.The hammer dogs are linked together by a yoke means causing them to movein unison and a cam or actuation means cooperating with the anvil andhammer dogs, is operative to tilt the hammer dogs inwardly to theirimpact positions once, each revolution of the hammer carrier. Anautomatic stop or limit means prevents them from tilting to the wrongimpact position in each direction of rotation. The dogs are proportionedand mounted so that they automatically swing to their non-impactpositions following an impact during rebound of the hammer dogs. Thisautomatic return of the hammer dogs to their non-impact positions iscaused by inertial forces resulting from the shape, mass and location ofthe dogs in conjunction with the rebound and subsequent acceleration ofthe dogs following their impact with the anvil. In addition, duringimpact of the dogs with the anvil, inertial forces act on the dogs toprevent their disengagement movement which would reduce the efiiciencyof the impact energy delivered to the anvil.

BRIEF DESCRIPTION OF DRAWINGS The invention is described in connectionwith the accompanying drawings wherein:

FIG. 1 is an elevational view of a rotary impact wrench having portionscut away to show the impact clutch of this invention in section;

FIGS. 2 to 5 are sections taken on corresponding lines 2-2 to 5--5 inFIG. 1;

FIG. 6 is a section taken on line 66 in FIG. 1 except that the hammerdogs are shown in their free or nonimpacting position;

FIG. 7 is an axial section taken on line 77 in FIG. 3;

FIGS. 8, 9 and 10 are schematic views showing the hammer dog, anvil andcam systems in sequential positions prior to and at the moment ofimpact;

FIGS. 11 to 13 are sequential views showing the hammer dog and anvilduring and following impact;

FIGS. 14 and 15 are schematic views similar to FIGS. 8 to 10illustrating the components when the impact mechanism is rotated in theopposite direction from that shown in FIGS. 8 to 10; and

FIG. 16 is a schematic view illustrating the path of the eccentric pinas it moves past the hammer cam tang and the hammer stop pin.

DESCRIPTION OF PREFERRED EMBODIMENT The rotary impact wrench 1 shown inFIG. 1 conventionally includes a casing 2 including a nose portion 3, amotor portion 4 and a handle portion 5. The nose portion 3 carries aspindle 6 projecting from its front end, the motor portion 4 houses anair motor having a drive shaft 7 and the handle portion carries an op ai g gg 8 and an inlet connection 9 adapted to be attached to an air hosefor feeding air to the motor. The spindle 6 carries flats 10 adapting itto be attached to a conventional wrench socket (not shown). All of theforegoing structure is conventional in the rotary impact wrench art.

The motor shaft 7 is connected to the wrench spindle by a novel rotaryimpact clutch 12 which is the subject of this invention. In general, theclutch 12 includes a hammer 14 rotating around an anvil 15. The hammer14 is driven by the motor shaft 7 and the anvil 15 is integrally fixedto the spindle 6.

The hammer 14 includes a hammer cage or carrier 17 having a rear plate18, a front plate 19 and a pair of interconntcting braces 20. The rearplate 18 is journaled on a stub shaft 21 at the rear end of the anvil15. This stub shaft 21 has a reduced diameter. The front plate 19 isjournaled on an enlarged annulus 22 provided on the forward portion ofthe anvil 15. To this point in the description, the hammer cage 17 isfree to rotate around the anvil 15.

The anvil 15 carries a pair of axially extending fanshaped jaws, teeth,detents or abutments 24 located diametrically opposite each other. Thesejaws 24 are positioned intermediate the rear and front plates 18 and 19of the hammer cage 17. In describing the jaws 24 as fan-shaped, it ismeant that they project generally radially outward from the anvil 15with their sides diverging outwardly like a sector of a cylinder. Thejaws 24 are adapted to receive rotary impacts or blows from the hammer14.

The hammer cage 17 carries a pair of arcuate shaped hammer dogs 25tiltably mounted on longitudinal pivot pins 26 extending between therear and front plates 18 and 19 of the cage 17. The hammer dogs 25 arelocated at opposite diametrical locations in the cage 17 with the cagebraces 20 positioned degrees from the pivot pins 26 so the dogs 25 arefree to tilt without interference with the braces 20. The hammer dogs 25carry radially diverging end surfaces 27 adapted to substantiallyconform to the jaws 24 on the anvil 15 so that they can tilt inwardly asshown in FIG. 5 and engage the jaws 24, to strike an impact or rotaryblow to the anvil 15. It will be noted that the surfaces 27 have aslight arcuate curve. The hammer dogs 25 have three positions includinga midposition as shown in FIG. 6, wherein the hammer 14 can rotatefreely around the anvil without the dogs 25 striking a blow, a clockwiseimpact position, as shown in FIG. 3, wherein the dogs 25 tilt forwardlyand inwardly to strike a blow in the clockwise rotary direction and acounterclockwise direction wherein they tilt forwardly and inwardly inthe counterclockwise direction. As shown FIG. 2, the rear plate 18 ofthe cage 17 is cruciform-shaped and has a pair of larger diametricallyextending arms 29 which carry the hammer dog pins 26. A driver fork 30is keyed to the motor shaft 7 and includes fingers 31 projectinglongitudinally forward between the cruciform-shaped projections of therear plate 18 of the hammer cage 17. The fingers 31 are positioned toengage the side edges of the large arms 29 on the cage rear plate 1 8 todrive the hammer 14. The fingers 31 are spaced to provide an amount oflost motion between the driver fork 30 and the hammer 14.

Each finger 31 of the driver fork 30 carries a stop pin 32, as shown inFIG. 7, projecting forward from the end of the finger 31 and adapted toengage against a shoulder 33, shown in FIG. 8, provided on the end of ahammer dog 25 to prevent the dog from tilting in the Wrong directionwhen rotating in a given direction. The lost motion of the driver fork30 on the hammer 14 allows the pins 32 to move from one stop position toanother relative to the hammer dogs 25 when the rotation of the hammer14 is reversed.

The hammer dogs 25 are interconnected by a barshaped yoke 35 having itsmiddle pivoted on the stub shaft 21 at the rear end of the anvil 15 andhaving diametrically extending arms carrying yoke pins 36. The

yoke pins 36 are straddled by bifurcated tongues 37 which are fixed toand project inwardly from the hammer dogs 25. The yoke 35 holds or locksthe hammer dogs 25 in identical positions. In addition, the yoke 35 canbe pivoted to move the hammer dogs 25 to their impact position. Thismovement is accomplished by a unique cam system.

The middle of the anvil carrying the jaws 24 is joined or interconnectedto the rear end stub shaft 21 by an anvil eccentric 39. An eccentricring 40 is journaled on the anvil eccentric 39 and carries a pair ofeccentric cam pins 41 located at diametrically opposed positions andprojecting rearwardly into the circular path of the yoke 36. One side ofthe yoke 35 carries a pair of hookshaped cams 44 located near theopposite ends of the yoke 35. The hammer cage rear plate 18 carries ahammer cam tang 45 projecting forward into the circular path of the yoke35 and the eccentric cam pins 41.

As the hammer rotates, the entire cam system rotates with it. Thisincludes the yoke 35, the eccentric ring 40 and the hammer cam tang 45.As the eccentric ring 40 rotates, it also orbits eccentrically aroundthe hammer axis. This eccentric movement will eventually cause the campins 41 to engage between an edge of the hammer cam tang 45 and a hookcam 44 on the yoke 35 forcing the yoke 35 to tilt the hammer dogsforwardly and inwardly to an impact position. The eccentric 39 ispositioned so that this tilting of the hammer dogs 25 will occur as theynear the jaws 24 on the anvil 15. This tilting of the hammer dogs 25inwardly to their impact position, will occur only once during a fullrevolution of the hammer 14. After the hammer dogs 25 are tiltedinwardly, the eccentric pins 41 release the yoke before the dogs 25impact the anvil jaws 24 so the dogs 25 are free to move to theirmid-position following impact.

The sequential FIGS. 8, 9 and 10 illustrate the operation of the camsystem. FIG. 8 shows a hammer dog 25 in its non-impact position passingover one of the anvil jaws 24 and about 100 degrees from its position ofimpact with the opposite anvil jaws 24. At this time, one of theeccentric pins 41 is beginning to engage a hook-shaped yoke cam 44 whilethe other eccentric pin 41 is engaging the hammer cam tang 45. Both ofthe eccentric pins 41 must engage their respective cam surfaces 44 and45 before they can apply any force in moving the hammer dogs 25 inwardlyto their impact positions.

As the hammer dog 25 continues to rotate, the yoke 35, the eccentricring and the hammer cam tang also rotates with the hammer dog 25. FIG. 9shows the hammer dog 25 about 30 degrees from its position of impactwith the anvil jaw 24. At this time the hammer dog is tilting inwardlytoward an impact position. This tilting movement is caused by thestationary eccentric 39 forcing the eccentric ring 40 to translate tothe left (as shown in FIG. 9) of the hammer axis 47 which forces theyoke 35 to rotate counterclockwise relative to the hammer dog a slightamount which is sufficient to tilt the dog 25 inwardly. As soon as thehammer dog 25 completes its inward tilting movement, which occurs on theinner peak of the hook-shaped cam 44, the cam 44 is contoured so as tostop the relative movement of the yoke 35 and the hammer cam tang 45releases its eccentric pin 45 so that the yoke 35 is free from theapplication of further tilting forces. The moment of release is selectedso that the hammer dog 25 is still tilting inwardly and will continuetilting inwardly until just before it strikes the anvil jaw 24 as shownin FIG. 10. In this way, the hammer dog 25 cannot begin tiltingoutwardly prior to impact with the anvil 15.

At the moment of impact, as shown in FIG. 10, the eccentric pins 41 aredisengaged from the hook-shaped yoke cam 44 and the hammer cam tang 45so that the hammer dog 25 is free to tilt outward following impact. Thehammer cage rear plate 18 carries a stop pin 48 located outwardly of thehammer cam tang 45 to prevent the eccentric ring 40 from rotating pastthe hammer cam tang 45 to the other side of the hammer cam tang duringrebound of the hammer dog 25 following impact.

At this point it may be well to more fully explain the action of thehammer dog 25 during impact and following the impact. The hammer dog 25is shaped and sized so that the surface 27 will not lock against theanvil jaw 24 in case the tool motor is started when these surfaces arein engagement. This is accomplished by sizing the hammer so that theengagement line of force action between the hammer dog surface 27 andthe anvil jaw will extend radially outward from the axis of the pivotpin 26. This force line is shown in FIG. 10 as dotted line 50 and isnormal to the line of engagement between the hammer dog surface 27 andthe anvil jaw 24. Due to the arcuate curvature of the surface 27, theengagement between the surface 27 and jaw 24 is limited to line contactextending generally parallel to the axis of the tool. Actually, thisline contact will be enlarged from a true line contact due to theresiliency of the metal surfaces. This engagement force line 50 iscalled a non-locking force line.

As a result of the non-locking force line 50, one could presume that theimpact engagement between the hammer dog 25 and the anvil jaw 24 wouldtend to cam these surfaces out of engagement and thereby reduce theefficiency of the impact blow. However, this is not true. Instead, thehammer dog 25 is subject to forces which tend to tilt it furtherinwardly at the moment of impact. This result is attributed to the factthat the center of percussion 49 of the hammer dog 25 is locatedradially outwardly from the engagement force line 50 and the axis of thepivot pin 26, as shown in FIG. 10.

In general, it can be said that the inertial forces of the hammer dog 25form a resultant force acting forwardly through the center of percussion49 of the hammer dog 25 at the moment of impact. This resultant forceacting through the center of percussion 49 is strong enough at theinstant of impact to overcome the force of engagement acting along theforce engagement line 50 and the torque force delivered by the pivot pin26 to form a force couple tending to tilt the hammer dog 25 furtherinwardly toward its impact position. This force couple is illustrated inFIG. 10 and is the combination of the resultant force acting through thecenter of percussion 49 and the moment arm of the resultant forcerelative to the axis of the hammer dog 25. The mass and proportions ofthe hammer dog 25 are such that will provide a sufficient resultantinertial force to prevent the hammer dog 25 from disengaging duringimpact.

FIGS. 11, 12 and 13 illustrate the sequence of movement of the hammerdog 25 following impact. FIG. 11 shows the hammer dog 25 at the momentof impact. FIG. 12 shows the hammer dog 25 during its reboundingmovement in a counterclockwise direction. Following impact, the hammerdog 25 is driven backwardly or rearwardly in a counterclockwisedirection, as a result of the resiliency of the elements placed understress by the impact. These elements will include the anvil 15, thesocket (not shown) attached to the spindle 6 and the fastener beingdriven by the wrench 1. At the same time, the motor is applying aclockwise torque force to the hammer dog 25 attempting to slow down itsrebounding travel and eventually to drive it forwardly in the clockwisedirection. The combination of these actions forms a force couple tendingto tilt the hammer dog 25 radially outward to its non-impact position.This force couple is explained as follows.

When the hammer dog 25 is moving in the rebounding direction, as shownin FIG. 12, and is subject to a deceleration force, inertial forces arecreated which form a resultant force acting rearwardly generally throughthe center of percussion 49. This deceleration or slow-down force isapplied by the motor through the axis of the pivot pin 26. These twoforces form a force couple which is illustrated in FIGS. 12 and 13.

This force couple continues to act on the hammer dog during its reboundand after it begins moving forward again. When the hammer dog 25 stopsmoving rearwardly, in the counterclockwise direction, its inertialforces resist acceleration by the pivot pin 26 to continue creating thesame force couple. This force couple causes the hammer dog 25 tocomplete its outward tilting movement to its non-impact position wellbefore the leading end 27 of the hammer dog 25 approaches and passes theanvil jaw 24 as shown in FIG. 13 so that the hammer dog 25 is free topass the anvil jaw 24 without again engaging it.

It should be clear that the action of the hammer dog 25 in automaticallytilting outwardly to its non-impact position following impact is theresult of locating the center of percussion of the hammer dog 25radially outwardly from the axis of the pivot pin 26.

At this time, we want to make it clear that the resultant force of thehammer dog 25 probably does not act exactly through the center ofpercussion 49 due to the effect of other mass forces connected in thehammer system. However, we have found that this resultant is near enoughto the center of percussion 49 to presume that it is at the center ofpercussion 49 for the purposes of explaining and claiming thisinvention. The center of percussion 49 has a definite relationship tothe center of mass of the hammer dog 25 and therefore this invention canalso be explained in terms of the center of mass.

Following impact, the hammer dog 25 will rotate one full turn about theanvil 15 before again impacting the anvil 15. This action is due to thefact that the cam system will only tilt the dogs 25 inwardly to theirimpact position once during each revolution of the hammer 14.

It should be noted that the hammer 14 can rebound two full turns beforestriking an impact in the reverse direction. Since the maximum reboundof a rotary impact tool is normally less than a one-half turn, thismechanism will never strike a reverse blow during rebound.

The reason why the mechanism will not strike a reverse blow during lessthan two full turns of rebound movement, will be understood byexplaining the movement of the hammer in a reverse direction.

If we assume that the clutch mechanism 12 is positioned as shown in FIG.and the motor is reversed, the hammer 14 will rotate in thecounterclockwise direction almost two full turns before the hammer dog25 is again tilted inwardly to strike the opposite side of the anvil jaw24. During one full turn, the eccentric ring 40 swings relativelyclockwise past the hammer stop pin 48. In order for this to occur, theeccentric ring 40 must be translated to the left as shown in FIG. 10 inorder for the eccentric pin 41 to clear the hammer stop pin 48 and thiscan only occur during one full revolution of the hammer 14 around theanvil.

FIG. 14 shows the eccentric pin 41 clearing the stop pin 48 during itsfirst revolution in the counterclockwise direction. FIG. 16 illustratesthe path of the eccentric pin 41 betwen its position shown in FIG. 10and the position shown in FIG. 15, when the hammer dog 25 strikes animpact to the anvil 15. After eccentric pin 41 clears the stop pin 48,it is captured in the concave rear side of the hammer tang 45 for aportion of the travel of the hammer 14. Finally, after the hammerrotates about one revolution, the eccentric pin will move to the left ofthe hammer tang 45, as shown in FIG. 16, wherein it can operate to tiltthe hammer dog 25 into impact position during the next revolution of thehammer 14.

One advantage of the requirement of two turns before striking the firstimpact blow, is that the motor can accelerate the hammer to a higherspeed to create a stronger first blow. This action can be useful inremoving fasteners when a very strong first blow is necessary to startmoving the fastener. If the first blow does not move the fastener, anoperator can again reverse the motor to rotate a few turns in theopposite direction and then reverse it to obtain another strong blow.This operation can be performed again and again when necessary. Thepoint is that the wrench is capable of providing a much stronger blowthan its normal blow or impact, and that this capability is useful attimes.

Although a single embodiment of the invention is illustrated anddescribed, it should be understood that the invention is not limitedthereto and that various changes may be made in the design andarrangement of the parts without departing from the spirit and scope ofthe invention as set forth in the claims.

I claim:

1. An impact mechanism comprising:

a rotary carrier adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a jaw;

a hammer dog movably mounted on said carrier adjacent said anvil andmovable radially inwardly from a first position wherein it clears saidanvil jaw as the carrier rotates around said anvil to a second positionwherein it will engage and strike a blow to said anvil jaw; and

actuation means interconnected between said anvil and hammer dog formoving said hammer dog inwardly to said second position to strike animpact blow to said anvil, said means allowing said hammer dog to passsaid anvil jaw without engaging it during a portion of the rotation ofsaid carrier following the striking of a blow.

2. The impact mechanism of claim 1 wherein:

said anvil carries a second jaw which is circumferentially spaced fromsaid first jaw and said actuation means allows said hammer dog to passsaid second jaw without striking it following an impact with said firstjaw.

3. An impact mechanism comprising:

a rotary carrier rotatably mounted on an axis and adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a radially projecting jaw;

a hammer dog pivoted on said carrier adjacent said anvil and movableradially inwardly from a first position wherein it clears said anvil jawas it rotates around said anvil to a second position wherein it willengage and strike a blow to said anvil jaw; and

actuation means interconnected between said anvil and hammer dog forswinging said hammer dog inwardly to said second position to strike animpact blow to said anwil, said means allowing said hammer dog to passsaid anvil jaw without engaging it during a portion of the rotation ofsaid carrier following the striking of a blow.

4. A rotary impact tool clutch mechanism comprising:

a rotary hammer carrier adapted to be driven by a rotary motor;

an anvil rotatably and coaxially mounted adjacent said hammer carrierand having a pair of diametrically opposed jaws;

a pair of hammer dogs movably mounted on said hammer carrier on theopposite sides of the hammer carrier axis and adapted to move inwardlyto strike simultaneous impact blows to said jaws on said anvil; and

actuation means interconnected between said anvil and hammer dogs forautomatically moving said hammer dogs inwardly as they approach saidanvil jaws to strike said impact blows, said means allowing said hammerdogs to pass said anvil jaws without engagement on the next time theyapproach said anvil jaws following the striking of said impact blows.

5. A rotary impact tool clutch mechanism comprising:

a rotary hammer carrier adapted to be driven by a rotary motor;

an anvil rotatably and coaxially mounted adjacent said hammer carrierand having a pair of diametrically opposed jaws;

a pair of hammer dogs pivotably mounted on said hammer carrier on theopposite sides of the hammer carrier axis and adapted to pivot inwardlyto strike simultaneous impact blows to said jaws on said anvil; and

actuation means interconnected between said anvil and hammer dogs forautomatically pivoting said hammer dogs inwardly as they approach saidanvil jaws to strike said impact blows, said means allowing said hammerdogs to pass said anvil jaws without striking impact blows during aportion of the rotation of the carrier following the striking of saidimpact blows.

6. The impact mechanism of claim wherein:

said anvil is surrounded by said carrier.

7. The impact mechanism of claim 6 wherein:

said hammer dogs are pivoted on axes which extend parallel to therotation axis of said hammer carrier.

8. The impact mechanism of claim 6 wherein:

said hammer dogs have non-impact positions wherein said hammer carriercan rotate around said anvil without said hammer dogs engaging saidanvil.

9. The impact mechanism of claim 8 wherein:

said hammer carrier includes front and rear plates journaled on portionsof said anvil.

10. An impact mechanism comprising:

a carrier rotatably mounted on an axis and adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a radially projecting jaw;

a hammer dog pivoted on said carrier adjacent to said anvil and tiltablebetween a middle and first position wherein it clears said anvil jaw asit rotates around said anvil, a second position wherein it will engageand strike a blow to said anvil jaw as said carrier rotates in aclockwise direction and a third position wherein it will engage andstrike a blow to said anvil jaw as said carrier rotates in acounterclockwise direction; and

limit means mounted on said carrier and operative to prevent said hammerdog from swinging to said third position when said carrier is driven ina clockwise direction.

11. The impact mechanism of claim 10 wherein:

said limit means also serves to drive said carrier.

12. The impact mechanism of claim 10 wherein:

said limit means is operative to prevent said hammer dog from swingingto said second position when said carrier is driven in acounterclockwise direction.

13. The impact mechanism of claim 12 wherein:

said limit means engages said carrier and includes a stop means adaptedto engage said hammer dog to prevent the hammer dog from moving to saidsecond or third positions depending upon the direction of rotation ofsaid carrier.

14. The impact mechanism of claim 13 wherein:

said limit means is a driver which engages said carrier for driving itin a manner providing a limited amount of rotary lost motion betweensaid driver and said carrier, whereby said stop means will move betweentwo different positions relative to said carrier depending on the rotarydriving direction of said driver.

15. The impact mechanism of claim 14 wherein:

said driver includes a pair of circularly spaced stop pins moving toalternate positions relative to said hammer dog in opposite drivingdirections of the carrier.

16. An impact wrench mechanism comprising:

a carrier rotatably mounted on an axis and adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a radially projecting jaw with an impact surface;

a hammer dog pivoted on said carrier on an axis extending substantiallyparallel to said carrier axis adjacent to said anvil and tiltableradially inward from a non-impact position to an impact position toengage said anvil jaw as said carrier rotates, said hammer dog having animpact surface adapted to impact said anvil jaw impact surface, and saidhammer dog being positioned, proportioned and having a mass and a centerof percussion location which will cause the creation of a resultantinertial force couple acting on said hammer dog during the rebound ofsaid hammer dog and carrier following an impact which will urge saidhammer dog to tilt outwardly to its non-impact position and to remain inthat position as the carrier begins rotation forward.

17. The impact mechanism of claim 16 including:

a second hammer dog similar to the first hammer dog pivoted on saidcarrier diametrically opposite said first hammer dog and a second jawsimilar to the first jaw located on said anvil diametrically relative tosaid first jaw.

18. An impact mechanism comprising:

a carrier rotatably mounted on an axis and adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a radially projecting jaw;

a hammer dog pivoted on said carrier adjacent said anvil and tiltablebetween a middle and first position wherein it clears said anvil jaw asit rotates around said anvil, a second position wherein it will engageand strike a blow to said anvil jaw as said carrier rotates in aclockwise direction and a third position wherein it will engage andstrike a blow to said anvil as said carrier rotates in acounterclockwise direction; and

actuation means interconnected between said anvil and hammer dog andoperative to tilt said hammer dog to said second position when saidcarrier is driven in a clockwise direction to cause said hammer dog tostrike an impact blow to said anvil jaw.

19. The impact mechanism of claim 18 wherein:

said actuation means is operative to tilt said hammer dog to said thirdposition when said carrier is driven in a counterclockwise direction tocause said hammer dog to strike an impact blow to said anvil jaw.

20. A rotary impact tool clutch mechanism comprising:

a rotary hammer carrier adapted to be driven by a rotary motor;

an anvil rotatably and coaxially mounted within said hammer carrier andhaving a pair of diametrically opposed jaws;

a pair of hammer dogs pivotably mounted on said hammer carrier on theopposite sides of the hammer cage axis and adapted to pivot inwardly tostrike simultaneous impact blows to said jaws on said anvil;

cam means interconnected between said anvil and hammer dogs forautomatically pivoting said hammer dogs inwardly as they approach saidanvil jaws to strike said impact blows, said cam means allowing saidhammer dogs to pass said anvil jaws without striking impact blows duringa portion of the rotation of the carrier following the striking of saidimpact blows and including a link member interconnecting said hammerdogs together for simultaneous rotation.

21. The impact tool mechanism of claim 20 wherein:

said cam means includes a cam surface on said anvil and interconnectingmeans interconnecting said cam surface to surfaces on said carrier andsaid link member to pivot said hammer dogs inwardly to impact position.

22. The impact tool mechanism of claim 21 wh r in:

said interconnecting means rotates on said anvil surface.

23. The impact tool mechanism of claim 22. wherein:

said cam surface is an eccentric fixed on said anvil and saidinterconnecting means is a ring journaled on said eccentric.

24. The impact tool mechanism of claim 23 wherein:

said link member is journaled on said anvil and rotates with said hammerdogs.

25. The impact tool mechanism of claim 24 wherein:

said ring journaled on said eccentric is disengaged from said surfaceson said carrier and said link member after said hammer dogs are pivotedinwardly and before said hammer dogs engage said jaws.

26. An impact mechanism comprising:

a carrier rotatably mounted on an axis and adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a radially projecting jaw;

a hammer dog pivoted on said carrier adjacent said anvil and tiltablebetween a middle and first position wherein it clears said anvil jaws asit rotates around said anvil, a second position wherein it will engageand strike a blow to said anvil jaw as said carrier rotates in aclockwise direction and a third position wherein it will engage andstrike a blow to said anvil as said carrier rotates in acounterclockwise direction; and

actuation means interconnected between said anvil and hammer dog andoperative to tilt said hammer dog to said second position when saidcarrier is driven in a clockwise direction to cause said hammer dog tostrike an impact blow to said anvil jaw at least once each completerevolution of said carrier;

said actuation means being operative to allow said car rier to rotatemore than one revolution before striking an impact when initiallyreversed after rotating in the opposite direction, thus enabling saidhammer dog to strike an initial impact which is substantially morepowerful than its normal impact.

27. An impact wrench mechanism comprising:

a carrier rotatably mounted on an axis and adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a radially projecting jaw;

a hammer dog pivoted on said carrier on an axis extending substantiallyparallel to said carrier axis adjacent to said anvil and tiltableradially inward to engage said jaw as said carrier rotates, said hammerdog being positioned and shaped so that it impacts said jaw generallyalong a force line displaced radially outward from the axis of thehammer dog pivot causing the creation of a camming force acting on thehammer dog tending to cause it to tilt outwardly to disengage said jawduring said impact, and said hammer dog being also positioned,proportioned and having a mass and a mass center location which willcause the creation of inertia forces acting on said hammer dog duringthe instant of said impact which will overcome said camming force andwill prevent said hammer dog from tilting outwardly during the instantof impact.

28. An impact wrench mechanism comprising:

carrier rotatably mounted on an axis and adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a radially projecting jaw with an impact surface;

a hammer dog pivoted on said carrier on an axis extending substantiallyparallel to said carrier axis adjacent to said anvil and tiltableradially inward to engage said jaw as said carrier rotates, said hammerdog having an impact surface adapted to engage said anvil jaw impactsurface, the impact surfaces of said hammer dog and anvil jaw beingshaped so that during the impact of said hammer dog with said anvil, acamming force is created acting on the hammer dog tending to cause it totilt outwardly to disengage said jaw during said impact, and said hammerdog being also positioned, proportioned and having a mass and a masscenter location which will cause the NILE C. BYERS, ]R.,

12 creation of inertia forces acting on said hammer dog during theinstant of said impact which will overcome said camming force and willprevent said hammer dog from tilting outwardly during the instant of impact.

29. An impact wrench mechanism comprising:

a carrier rotatably mounted on an axis and adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a radially projecting jaw with an impact surface;

a hammer dog pivoted on said carrier on an axis extending substantiallyparallel to said carrier axis adjacent to said anvil and tiltableradially inward to engage said jaw as said carrier rotates, said hammerdog having an impact surface adapted to engage said anvil jaw impactsurface, the impact surfaces of said hammer dog and anvil jaw beingshaped so that during the impact of said hammer dog with said anvil, acamming force is created acting on the hammer dog tending to cause it totilt outwardly to disengage said jaw during said impact, and said hammerdog being also positioned, proportioned and having a mass and a centerof percussion location which will cause the creation of a resultantinertial force couple acting on said hammer dog during the instant ofsaid impact which will prevent said hammer dog from tilting outwardlyduring the instant of impact.

30. An impact wrench mechanism comprising:

a carrier rotatably mounted on an axis and adapted to be driven;

an anvil rotatably and coaxially mounted adjacent said carrier andhaving a radially projecting jaw with an impact surface;

a hammer dog pivoted on said carrier on an axis extending substantiallyparallel to said carrier axis adjacent to said anvil and tiltableradially inward to engage said jaw as said carrier rotates, said hammerdog having an impact surface adapted to engage said anvil jaw impactsurface, the impact surfaces of said hammer dog and anvil jaw beingshaped so that during the impact of said hammer dog with said anvil, acamming force is created acting on the hammer dog along a force linelocated relative to the hammer dog axis to cause it to tilt outwardly todisengage said jaw during said impact, and said hammer dog being alsopositioned, proportioned and shaped to have a center of percussionlocation which provides a greater moment arm about said hammer dog axisfor an inertial force opposing said camming force and acting throughsaid center of percussion than the moment or of said camming force aboutsaid hammer dog axis.

31. The impact wrench mechanism of claim 28 where- References CitedUNITED STATES PATENTS 5/1939 Jimerson 173-93.6 6/1942 Amtsberg 17393.-55/1959 Madsen 173-935 8/1964 Reynolds 173-935 4/1968 Kaman 173-93.56/1942 Amtsberg 173--93.5

Primary Examiner

